In the field of automobile technology, there has recently developed an ever more frequent demand that electric components such as e.g. pumps and actuators, should be able to return to the engine control device a feedback message indicating states of the components. Normally, these components are driven by the engine control device through pulse width modulation. This is performed via a sole existing signal line which serves both for transmission of the desired signal in the form of a PWM coding from the engine control device to the control unit of the component and which, conversely, shall also be used for communicating a possibly existing fault state or actual state of the component to the engine control device.
Such feedbacks of states for diagnostic purposes are known as far as the component will tie the signal line to ground if any fault is present. This will be detected by the engine control device because this device is used as a master. At the same time, the engine control device will measure the voltage on the signal line so that, if the engine control device tries to output a high level while, however, the line remains on a low level because of the ground connection, this will indicate that either the component does not work properly or the line is short-circuited. In the past, for this reason, the switching of the signal line to ground as performed by the electric component has commonly been used to communicate to the engine control device that a fault has occurred.